1. Field of the Invention
The invention relates to an erasing device, more particularly to an automatic erasing device for erasing chalk marks from a writing board by water.
2. Description of the Related Art
Referring to FIGS. 1 and 2, in co-pending U.S. patent application Ser. No. 09/170,942 filed by the applicant, now U.S. Pat. No. 6,073,297 an automatic erasing device 1 is disclosed to include an erasing mechanism adapted to be mounted on a writing board 10 for erasing chalk marks on the writing board 10. The writing board 10 has left and right end portions that extend in a longitudinal axis thereof and an intermediate portion between the left and right end portions.
As illustrated, the erasing mechanism includes an elongated housing 11 disposed frontwardly of and slidable relative to the writing board 10. The elongated housing 11 extends in a transverse axis relative to the longitudinal axis, and has upper and lower portions, a rear wall formed with an elongated rear opening 111 to confront the writing board 10, a front wall and an accommodating space 13 defined between the front and rear walls, and between the upper and lower portions. The elongated rear opening 111 extends from the upper portion to the lower portion. Upper and lower axles 132 are journalled in the elongated housing 11 proximate to the upper and lower portions, respectively. The axles 132 extend parallel to the longitudinal axis. A transmitting belt 133 is trained on the upper and lower axles 132 under tension, and is rotated upon rotation of the upper and lower axles 132 for movement along a rear route proximate to and in alignment with the elongated rear opening 111, and a front route parallel to the rear route and distal to the elongated rear opening 111. A plurality of eraser members 134 are disposed detachably on, and are spaced apart from one another along a circumferential outer surface of the transmitting belt 133. Each of the eraser members 134, when moving along the rear route, protrudes outwardly and rearwardly of the rear wall via the elongated rear opening 111 and is adapted to abut against the writing board 10. A driving motor 131 is disposed to drive either one of the upper and lower axles 132 so as to move the eraser members 134 along the front and rear routes. The elongated housing 11 is driven to move reciprocally in the longitudinal axis between the left and right end portions of the writing board 10, and is biased by two biasing units 17 toward the writing board 10 while the elongated housing 11 is being moved reciprocally in the longitudinal axis. Each of the biasing units 17 includes a shaft 170 disposed transversely between left and right walls of the elongated housing 11 and guided to move in an urging direction towards the rear opening 111, a roller 171 rotatably mounted on the shaft 170 by means of a screw 173, and a spring member 174 mounted by means of a spring retention unit 172 to bias the shaft 170 to move in the urging direction so as to bring the roller 171 to abut against the transmitting belt 133. An additional biasing unit 12 is provided to enhance contact between the eraser members 134 and the writing board 10 when the eraser members 134 are aligned with the rear opening 111 in the elongated housing 11. Preferably, the front wall of the elongated housing 11 is provided with a plurality of spaced scrubbing brushes 15 thereon in alignment with and capable of scrubbing the eraser members 134 when the latter are moved along the front route. The housing 11 further has a detachable front cover 14, and a dustbin 16 provided at the lower portion thereof and in communication with the accommodating space 13 by a connecting pipe 161 for collecting the chalk powder that results when the chalk marks are erased by the eraser members 134.
Some of the disadvantages that result from the use of the aforesaid erasing device 1 are as follows:
(i) The eraser members 134, though scrubbed by the brushes 15, can not wipe the chalk marks thoroughly from the writing board 10 after long term use. The chalk marks more or less adhere on the eraser members 134, thereby resulting in a poor wiping effect. PA1 (ii) Constant rubbing of the accumulated chalk on the eraser member 134 against the writing board 10 may hinder smooth reciprocal movement of the elongated housing 11 along the longitudinal direction, and subsequently result in the generation of noise.